Env variable for explicitly excluding cpython in participating during build

README.md

@@ -2,9 +2,9 @@
 
 ## `docker.io/paketobuildpacks/node-engine`
 
-The Node Engine CNB provides the Node binary distribution.  The buildpack
+The Node Engine CNB provides the Node binary distribution. The buildpack
 installs the Node binary distribution onto the `$PATH` which makes it available
-for subsequent buildpacks and in the final running container.  Examples of
+for subsequent buildpacks and in the final running container. Examples of
 buildpacks that might use the Node binary distribution are the [NPM
 CNB](https://github.com/paketo-buildpacks/npm) and [Yarn Install
 CNB](https://github.com/paketo-buildpacks/yarn-install)
@@ -148,6 +148,13 @@ the `BP_NODE_PROJECT_PATH` environment variable at build time either directly
 file](https://github.com/buildpacks/spec/blob/main/extensions/project-descriptor.md).
 This could be useful if your app is a part of a monorepo.
 
+### Exclude python installation during the build process
+
+To exclude the participation of the cpython during the build process, please use
+the `BP_NODE_EXCLUDE_BUILD_PYTHON` environment variable at build time either directly (ex. `pack build my-app --env BP_NODE_EXCLUDE_BUILD_PYTHON`).
+
+This will skip the installation of python during the build process on the build base image, by not requiring the cpython buildpack through the build plan.
+
 ### Enabling Inspector for Remote Debugging
 
 To enable the Inspector set the `BPL_DEBUG_ENABLED` environment variable at launch time. Optionally, you can specify the `BPL_DEBUG_PORT` environment variable to use a specific port.
@@ -162,11 +169,13 @@ For more information on debugging, see [Official Documentation](https://nodejs.o
 ## Run Tests
 
 To run all unit tests, run:
+
 ```
 ./scripts/unit.sh
 ```
 
 To run all integration tests, run:
+
 ```
 /scripts/integration.sh
 ```

detect.go

@@ -83,10 +83,21 @@ func Detect(nvmrcParser, nodeVersionParser VersionParser) packit.DetectFunc {
 			})
 		}
 
+		bpNodeExcludeBuildPython, bpNodeExcludeBuildPythonExists := os.LookupEnv("BP_NODE_EXCLUDE_BUILD_PYTHON")
+		excludePython := false
+		if bpNodeExcludeBuildPythonExists && (bpNodeExcludeBuildPython == "" || bpNodeExcludeBuildPython == "true") {
+			excludePython = true
+		}
+
+		_, pythonNotFoundErr := exec.LookPath("python")
+		_, python2NotFoundErr := exec.LookPath("python2")
+		_, python3NotFoundErr := exec.LookPath("python3")
+
+		pythonFound := (pythonNotFoundErr == nil || python2NotFoundErr == nil || python3NotFoundErr == nil)
+
 		targetOs := os.Getenv("CNB_TARGET_DISTRO_NAME")
-		_, pythonNotFound := exec.LookPath("python")
 
-		installPython := (targetOs != "rhel" && pythonNotFound != nil)
+		installPython := (targetOs != "rhel" && !pythonFound && !excludePython)
 		if installPython {
 			requirements = append(requirements, packit.BuildPlanRequirement{
 				Name: Cpython,

detect_test.go

@@ -279,6 +279,161 @@ func testDetect(t *testing.T, context spec.G, it spec.S) {
 		})
 	})
 
+	context("when $BP_NODE_EXCLUDE_BUILD_PYTHON is NOT set", func() {
+		var pathEntries string
+		it.Before(func() {
+			pathEntries = os.Getenv("PATH")
+			os.Setenv("PATH", "")
+		})
+
+		it.After(func() {
+			os.Setenv("PATH", pathEntries)
+		})
+		it("and python does NOT exist on the path, it includes cpython buildpack", func() {
+
+			result, err := detect(packit.DetectContext{
+				WorkingDir: "/working-dir",
+			})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result.Plan).To(Equal(packit.BuildPlan{
+				Provides: []packit.BuildPlanProvision{
+					{Name: nodeengine.Node},
+				},
+				Requires: []packit.BuildPlanRequirement{
+					{
+						Name: nodeengine.Cpython,
+						Metadata: nodeengine.BuildPlanMetadata{
+							Build:  true,
+							Launch: false,
+						},
+					},
+				},
+				Or: []packit.BuildPlan{
+					{
+						Provides: []packit.BuildPlanProvision{
+							{Name: nodeengine.Node},
+							{Name: nodeengine.Npm},
+						},
+						Requires: []packit.BuildPlanRequirement{
+							{
+								Name: nodeengine.Cpython,
+								Metadata: nodeengine.BuildPlanMetadata{
+									Build:  true,
+									Launch: false,
+								},
+							},
+						},
+					},
+				},
+			}))
+
+		})
+	})
+
+	context("when $BP_NODE_EXCLUDE_BUILD_PYTHON is NOT set", func() {
+
+		var pathEntries string
+		it.Before(func() {
+			pathEntries = os.Getenv("PATH")
+			os.Setenv("PATH", pathEntries+":/some/path/to/python")
+		})
+
+		it.After(func() {
+			os.Setenv("PATH", pathEntries)
+		})
+		it("and python does exists on the path, it does NOT include on the plan", func() {
+
+			result, err := detect(packit.DetectContext{
+				WorkingDir: "/working-dir",
+			})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result.Plan).To(Equal(packit.BuildPlan{
+				Provides: []packit.BuildPlanProvision{
+					{Name: nodeengine.Node},
+				},
+				Or: []packit.BuildPlan{
+					{
+						Provides: []packit.BuildPlanProvision{
+							{Name: nodeengine.Node},
+							{Name: nodeengine.Npm},
+						},
+					},
+				},
+			}))
+		})
+	})
+
+	context("when $BP_NODE_EXCLUDE_BUILD_PYTHON is set", func() {
+		var pathEntries string
+		it.Before(func() {
+			pathEntries = os.Getenv("PATH")
+			os.Setenv("BP_NODE_EXCLUDE_BUILD_PYTHON", "true")
+			os.Setenv("PATH", "")
+		})
+
+		it.After(func() {
+			os.Setenv("PATH", pathEntries)
+			os.Unsetenv("BP_NODE_EXCLUDE_BUILD_PYTHON")
+		})
+
+		it("and python does NOT exist on the path, it does NOT include cpython buildpack", func() {
+
+			result, err := detect(packit.DetectContext{
+				WorkingDir: "/working-dir",
+			})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result.Plan).To(Equal(packit.BuildPlan{
+				Provides: []packit.BuildPlanProvision{
+					{Name: nodeengine.Node},
+				},
+				Or: []packit.BuildPlan{
+					{
+						Provides: []packit.BuildPlanProvision{
+							{Name: nodeengine.Node},
+							{Name: nodeengine.Npm},
+						},
+					},
+				},
+			}))
+		})
+
+	})
+	context("when $BP_NODE_EXCLUDE_BUILD_PYTHON is set", func() {
+
+		var pathEntries string
+		it.Before(func() {
+			pathEntries = os.Getenv("PATH")
+			os.Setenv("BP_NODE_EXCLUDE_BUILD_PYTHON", "true")
+			os.Setenv("PATH", pathEntries+":/some/path/to/python")
+		})
+
+		it.After(func() {
+			os.Setenv("PATH", pathEntries)
+			os.Unsetenv("BP_NODE_EXCLUDE_BUILD_PYTHON")
+		})
+		it("and python exists on the path, it does NOT include cpython buildpack", func() {
+
+			result, err := detect(packit.DetectContext{
+				WorkingDir: "/working-dir",
+			})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result.Plan).To(Equal(packit.BuildPlan{
+				Provides: []packit.BuildPlanProvision{
+					{Name: nodeengine.Node},
+				},
+				Or: []packit.BuildPlan{
+					{
+						Provides: []packit.BuildPlanProvision{
+							{Name: nodeengine.Node},
+							{Name: nodeengine.Npm},
+						},
+					},
+				},
+			}))
+
+		})
+	})
+
 	context("failure cases", func() {
 		context("when the dir specified by BP_NODE_PROJECT_PATH does not exist", func() {
 			var workingDir string

integration/inspector_test.go

@@ -52,10 +52,12 @@ func testInspector(t *testing.T, context spec.G, it spec.S) {
 		image, logs, err = pack.WithNoColor().Build.
 			WithPullPolicy("never").
 			WithBuildpacks(
-				settings.Buildpacks.Cpython.Online,
 				settings.Buildpacks.NodeEngine.Online,
 				settings.Buildpacks.Processes.Online,
 			).
+			WithEnv(map[string]string{
+				"BP_NODE_EXCLUDE_BUILD_PYTHON": "",
+			}).
 			Execute(name, source)
 
 		Expect(err).NotTo(HaveOccurred())

integration/openssl_test.go

@@ -67,13 +67,13 @@ func testOpenSSL(t *testing.T, context spec.G, it spec.S) {
 
 				image, logs, err = pack.WithNoColor().Build.
 					WithBuildpacks(
-						settings.Buildpacks.Cpython.Online,
 						settings.Buildpacks.NodeEngine.Online,
 						settings.Buildpacks.BuildPlan.Online,
 					).
 					WithPullPolicy("never").
 					WithEnv(map[string]string{
-						"BP_NODE_VERSION": "20.*.*",
+						"BP_NODE_VERSION":              "20.*.*",
+						"BP_NODE_EXCLUDE_BUILD_PYTHON": "",
 					}).
 					Execute(name, source)
 				Expect(err).ToNot(HaveOccurred(), logs.String)
@@ -107,13 +107,13 @@ func testOpenSSL(t *testing.T, context spec.G, it spec.S) {
 
 				image, logs, err = pack.WithNoColor().Build.
 					WithBuildpacks(
-						settings.Buildpacks.Cpython.Online,
 						settings.Buildpacks.NodeEngine.Online,
 						settings.Buildpacks.BuildPlan.Online,
 					).
 					WithPullPolicy("never").
 					WithEnv(map[string]string{
-						"BP_NODE_VERSION": "20.*.*",
+						"BP_NODE_VERSION":              "20.*.*",
+						"BP_NODE_EXCLUDE_BUILD_PYTHON": "",
 					}).
 					Execute(name, source)
 				Expect(err).ToNot(HaveOccurred(), logs.String)

integration/optimize_memory_test.go

@@ -53,11 +53,13 @@ func testOptimizeMemory(t *testing.T, context spec.G, it spec.S) {
 		image, logs, err = pack.WithNoColor().Build.
 			WithPullPolicy("never").
 			WithBuildpacks(
-				settings.Buildpacks.Cpython.Online,
 				settings.Buildpacks.NodeEngine.Online,
 				settings.Buildpacks.Processes.Online,
 			).
-			WithEnv(map[string]string{"BP_NODE_OPTIMIZE_MEMORY": "true"}).
+			WithEnv(map[string]string{
+				"BP_NODE_OPTIMIZE_MEMORY":      "true",
+				"BP_NODE_EXCLUDE_BUILD_PYTHON": "",
+			}).
 			Execute(name, source)
 
 		Expect(err).NotTo(HaveOccurred())

integration/project_path_test.go

@@ -60,12 +60,12 @@ func testProjectPath(t *testing.T, context spec.G, it spec.S) {
 			image, logs, err = pack.WithNoColor().Build.
 				WithPullPolicy("never").
 				WithBuildpacks(
-					settings.Buildpacks.Cpython.Online,
 					settings.Buildpacks.NodeEngine.Online,
 					settings.Buildpacks.BuildPlan.Online,
 				).
 				WithEnv(map[string]string{
-					"BP_NODE_PROJECT_PATH": "hello_world_server",
+					"BP_NODE_PROJECT_PATH":         "hello_world_server",
+					"BP_NODE_EXCLUDE_BUILD_PYTHON": "",
 				}).
 				Execute(name, source)
 			Expect(err).ToNot(HaveOccurred(), logs.String)

integration/provides_test.go

@@ -55,10 +55,12 @@ func testProvides(t *testing.T, context spec.G, it spec.S) {
 			image, logs, err = pack.WithNoColor().Build.
 				WithPullPolicy("never").
 				WithBuildpacks(
-					settings.Buildpacks.Cpython.Online,
 					settings.Buildpacks.NodeEngine.Online,
 					settings.Buildpacks.BuildPlan.Online,
 				).
+				WithEnv(map[string]string{
+					"BP_NODE_EXCLUDE_BUILD_PYTHON": "",
+				}).
 				Execute(name, source)
 			Expect(err).ToNot(HaveOccurred(), logs.String)